Low frequency oscillator utilizing saturable magnetic timing core



Sept. 17, 1963 J. c. FREEBORN LOW FREQUENCY OSCILLATOR UTILIZINGSATURABLE MAGNETIC TIMING CORE Filed Dec. 21, 1961 I N V EN TOR. Jomv aFkzzaoe v ATTORNEY United States Patent 3,164,333 LUW FREQUENCY0SILLATOR UTILIZING SATURABLE MAGNETIC TIMING QORE John Freeborn,Woodland, Calit, assignor to Minneapohs-Honeywell Regulator Company,Minneapolis,

Minn a corporation of Delaware Filed Dec. 21, 1961, Ser. No. 161,232 6Claims. (tCi. 307-885) This invention relates to a precision lowfrequency or long interval oscillator and more specifically to a novelsemiconductonmagnetic core low frequency oscillator.

It is an object of this invention to provide an improved low frequencysemiconductor-magnetic core oscillator.

It is another object of this invention to provide a low frequencysemiconductor-magnetic core oscillator utilizing a slightly unbalancedA.C. source to cause saturation of the magnetic core and a saturationfeedback circuit for sensing core saturation and there-upon quicklydrive the magnetic core into full saturation by blocking the half cycleof unbalanced alternating current that would normally tend to drive thecore back out of saturation. Saturation of the magnetic core causes aswitching signal to a bistable circuit which reverses the polarity ofthe A.C. unbalance each time core saturation is reached.

These and other objects of the invention will become more apparent upona further consideration of the specifioation, claims and drawing ofwhich:

The single FIGURE of the drawing is a schematic representation of apreferred embodiment of the invention.

Referring now to the figure, the oscillator system cornprises in a broadsense the following major components including a driving transformer 10,a magnetic timing core 11, a saturation feedback circuit 12, asaturation feedback unlocking circuit 13 and a bistable switchingcircuit 14. Referring to the circuit components in detail, a pair ofpower input terminals 20 and 21 are connected to a suitable source ofregulated alternating current potential. The terminal 20 is connected bya conductor 22 to a primary winding 23 of the driving transformer 10,which transformer also includes a secondary winding 24. The opposite endof winding 23 is connected by a conductor 25 to one terminal 26 of asaturation feedback circuit 12. Power input terminal 21 is connected bya conductor 27 to the opposite terminal 39 of a saturation feedbackcircuit 12. V

A direct current path may be traced from the terminal 36) to a conductor31, a resistor 32, a junction 33, a diode 34 to a collector 35 of asemiconductor current controlling device, here shown as an npntransistor 36. The transistor 36 also includes a base electrode 37 andan emitter electrode 38, which emitter electrode 38 is connected by aconductor 40 to the terminal 26. Another current path may be traced fromthe terminal 26 through the conductor 40' to a junction 41, aresistor42, a junction 43, a diode 44 to a collector electrode 45 ofanother semiconductor current controlling device 46, similar to thedevice 36. The transistor 46 also includes a base electrode 47 and anemitter electrode 48, which emitter electrode is connected by aconductor 50 to a junction 51 on'the conductor 31. The diode 34 andtransistor 36 are poled to allow current flow from terminal 30 toterminal 26, and the diode 44 and transistor 46 are poled to allowcurrent flow in the opposite direction from terminal 26 to terminal 30.

Connected in parallel with the resistor 32 is a circuit which commencesata junction 52 on conductor 31 and can be traced through a capacitor53, a junction 54, and a rectifying diode 55 to the junction 33.Similarly, connected in parallel with the resistor 42 a circuit may betraced from :a junction 56 on the conductor 40 through a 2 capacitor 57,a junction 60 and a rectifying diode 59 to the junction 43. A conductor61 connects the base electrode 37 of transistor 36 to the junction 60,and a conductor 62 connects the junction 54 to the base electrode 47 oftransistor 46. A bias circuit for the transistor 36 comprises a junction64 on the conductor 61, a resistor 65 and a bias battery 66 to ajunction 67 on the conductor 40. The battery is polarized in a directionto normally render transistor 36 conductive. A bias circuit for normallyrendering transistor 46 conductive may also be traced from a junction 70on the conductor 62 through a resistor 71 and -a bias battery 72 to ajunction 73 on the conductor 31.

Referring now to the bistable circuit 14, a suitable source of directcurrent potential, such as a battery 80, has its positive terminalconnected to a conductor 81 and its negative terminal to a conductor 82which terminates at a junction 83. The conductor 81 is connected througha resistor 84 and a series of junctions 85, 86 and 87 to a collectorelectrode 90 of an npn type junction transistor 91. The transistor 91also includes a base electrode 92 and an emitter electrode 93, theemitter electrode 93 being connected by means of a junction 94 and abiasing resistor 95 to the junction 83.

The opposite current path in the bistable circuit 14 may be traced froma junction 96 on the conductor 81 through a resistor 97 and a series ofjunctions 100, 191 and 102 to a collector electrode 103- of a transistor104 which is of the same type as transistor 91. The transistor 104 alsoincludes [a base electrode 195 and an emitter electrode 196, the emitterelectrode 106 being directly connected to the junction 94 and theemitter 93.

A regenerative feedback circuit may be traced from the collector 90 oftransistor 91 to the base electrode 165 of transistor 104 from thejunction 86 through a resistor 110, a junction 111, a conductor 112, anda junction 113 which is connected to base 105. A capacitor 114 isconnected between the junctions 85 and 111 paralleling the resistor 110.In similar fashion, a regenerative feedback cirouit is connected betweenthe collector electrode 103 and the base electrode 92, which circuit maybe traced from junction 101 through a resistor 115, a junction 116, aconductor 117 and a junction 120 to the base electrode 92. A capacitor121 is connected from j'unction 161) to junction 116 parallelingresistor 115.

A bias circuit from the base 92 of transistor 91 may be traced from thejunction 120 through a resistor 122 to the junction 83. A similar biascircuit may be traced from the base 105 through the junction 113 and aresistor 123 to the junction 83.

A signal input circuit for the bistable circuit may be traced from theconductor 41} through a coupling capacitor 124 and a conductor 125 tothe junction 120, and another input circuit may be traced from theconductor 31 through a coupling capacitor 126 and the conductor 127 tothe junction 113.

An output circuit exists from the bistable circuit 14 which may betraced from the collector electrode 90 and junction 87 through aconductor 130, a junction 131, a relatively low resistance 132, ajunction 133, a relatively high resistance 134, and a conductor to thejunction 102 and collector electrode 103. In connection with theresistor 132, a circuit may be traced from junction 133 through aconductor 136, the secondary winding 24- of driving transformer 10, aconductor 137 and a winding 140 on the saturabletiming toroid 11 to thejunction 131. The magnetic timing core 11 is designed to have asubstantially rectangular hysteresis loop.

The saturation feedback unlocking circuit 13 comprises a pair oftransistors and 151, with transistor 150 having a collector eelctrode152, a base electrode 3 153, and an emitter electrode 154, thetransistor 151 including a base electrode 155, a collector electrode156, and an emitter electrode 157. The collector electrode 152 isdirectly connected to a junction 160 on the conductor 40, and thecollector electrode 156 is directly connected to a junction 161 on theconductor 31. Emitter 'electrodef154 is connected by a conductor 162 anda junction 163 to the base electrode 155, and emitter 157 is connectedby a conductor 164 and a junction 156 to the base electrode 153. Thejunction 165 is connected by a resistor 166 and a capacitor 167 to thejunction 87 in the bistable circuit 14. .The junction 163 is connectedby a conductor 17d to a junction 171 on the conductor 135. Inconsidering the operation of my invention, the operation will first bediscussedpin relatively general terms followed by a more specificdescription. In my invention a low frequency oscillator is provided byenergizing a saturable magnetic core with both an A.C.-potential and aD.C. potential; The two potentials may be considered as beingsuperimposed. The magnitude of the alternating current potential appliedto the core should be large enough to cause a change in the flux of thecore along a minor hysteresis loop but should be relatively smallcompared to the potential required to cause the core flux to follow theexcursion of the major hysteresis loop. The direct current potentialapplied to the core is of relatively small magnitude compared to theA.C. applied thereto. Neither the A.C. potential nor the DC. potentialis capable, by itself, of saturating the timing core. I

The energization of the core by A.C. and DC. has the effect ofincreasing the magnitude of one half cycle of the A.C. and decreasingthe succeeding half cycle or, in other words, unbalancing or offsettingthe A.C. which results in the core flux slowly moving towards saturationin a series of minor hysteresis loops. The driving transformer It}serves to isolate'unbalancing influences caused by component variationand other direct current deviations in the alternating current source.The saturation of timing toroid 11 serves to time the period ofoscillation cases for the low frequency magnetic oscillator. Thebistable flip-flop circuit 14 is effective to reverse the polarity ofthe direct current unbalance voltage applied to the timing toroid 11upon saturation being reached. The function of saturation feedbackcircuit 12 is to sense the beginning of saturation of timing toroid 11and to block the half cycle of unbalanced alternating current that wouldnormally drive the toroid back out of saturation thereby quickly drivingthe system into saturation. The saturation feedback unlocking circuit 13functions to nullify the action of the saturation feedback circuit bypermitting the system to come out of saturation after the half cycle hasbeen completed.

current drive fed to the timing toroid 11 through the drivingtransformer 10. The DC. level introduced by this resistor is in themillivoltarange and would not in itself be sufficient to saturate thetiming core. The A.C. potential supplied by the driving transformer issufficient to cycle the core in a minor hysteresis loop and appears tothe core 11 to be unbalanced due to the superimposed, millivolt levelDC. potential. Since neither the DC. unbalance nor the A.C. drive iscapable of saturating the timing core, numerous minor traversions of thehysteresis loop are required, and since the A.C. fed to the timing coreis unbalanced by the drop across resistor 132, each traverse of the BHcurve moves the step closer to the saturation point.

When the timing core 11 reaches saturation level its impedance decreasesand the current in one half'cycle of A.C. is increased. This increase isreflected to the primary winding 23 of the driving transformer 10 andthe saturation feedback circuit conducts more heavily on that halfcycle. Let it be assumed that during the half cycle when terminal 21 ispositive and current is flowing through resistor 32, diode 34 andtransistor 36, saturation level is reached and the current of this halfcycle is increased. This increase of current results in enough voltagedrop across the resistor 32 to overcome the threshold of normallynonconductive diode and charge capacitor 53. This charge on capacitor 53is negative at junction 54 with respect to junction 52 and produces aback bias on transistor 46 during a portion of the succeeding halfcycle. The fact that transistor 46 is made nonconductive for a portionof the said succeeding "voltage across junctions 26 and 30. The low A.C.level Referring now to the operation of the circuit in more 7 detail,the saturation feedback circuit transistors 36 and 46 are normallybiased to conduction by the bias supplies 66 and 72, respectively.During the half cycle when terminal 21 isvpositive, the alternatingcurrent flows through conductors 27 and 31, resistor 32, diode 34,transistor 36, conductors 40 and 25, winding 23 and coni I ductor 22; onthe succeeding half cycle when terminal 21 is negative, the currentflows through conductor 22, primary winding 23, resistor 42, diode 44,and transistor The voltage drop across resistor 132 is provided for thetiming core 11 by means of the voltage divider resistors 132 and 134connected across the collector electrodes Y46 and conductors 50, 31 and27. Transistor 36, diode across this circuit prior to saturation is notenough to trip the bistable circuit 14, but when saturation occurs arelatively large A.C. signal appears across the circuit which issufiicient to trip the bistable cincuit 14. This relatively large A.C.voltage is coupled through capacitors 124 and 126 to the base electrodes92 and of transistors 91 and 1194, respectively. The A.C. developed,

across this saturation feedback circuit 12 is again nearly symmetricalbecause the forward bias on 'the conducting transistor 36, as describedabove, is of low magnitude and when the driving transformer 10 issatunated the series impedance is so low that the transistor 36 cannotconduct a relatively high current dictated by the applied voltage andthe series impedance. It is this half cycle of voltage which appearsacross the con-ducting transistor 36 which is used to trigger thebistable circui-t14 to its opposite' mode.

When the bistable circuit '14 switches, it acts on transistors and 151of the saturation feedback unlocking circuit 13 to temporarily bypassthe blocking actiondescribed above and permits the driving transformer10 to return to its nonsatunate'd condition.

In other words, the saturation feedback unlocking transistors 150and-151 performs a shunting action across the o transistor 46 at thetime of bistable switching.

comprising resistor 166 and capacitor 167 and transistor 150 from baseelectrode 153 to emitter electrode 154 to junction 1412. This provides acurrent path through transistor 150 from collector 152 to emitterelectrode 154 and through the lbilSfisOOllCCtOI' junction of transistor151, thus eifectively shunting the off transistor 46 and momentarilynullifies the action of the saturation feedback circuit permitting thedriving transformer to come out of saturation and again act as a sourcefor the timing cor-e. Transistor 46 again becomes conductive.

As was mentioned, the DC. unbalance voltage across the bistable circuithas been reversed such that junction 37 is positive with respect tojunction 102, thereby reversing the polarity of DO across resistor 132such that junction 131 is positive with respect to junction 133. Sincethe direction of the DC. across resistor 132 is reversed, the timingcore 11 is gradually driven towards saturation in the opposite directionin a series of minor hysteresis loops.

Upon saturation being reached in the opposite direction, which willoccur during the half cycle when terminal 21 is negative, the currentthrough resistor 42, diode 44 and transistor 46 will increase. Theincreased voltage drop across resistor 42 then exceeds the threshold ofdiode 59 and it will conduct to charge capacitor 57. This charge oncapacitor 57 will be effective to render transistor 36 nonconductive inthe same manner previouslydescribed for transistor 46. The output signalfrom the saturation feedback circuit 12 will now trigger the bistableoircuit 1 1 back to its original mode in which transistor 91 againbecomes conductive. The unlocking circuit 13 will again operatesubstantially as described above but with transistor 151 conductive tobypass transistor 36. This polanity reversal thus occurs every time themagnetic core is saturated and serves to start the tra versions of thehysteresis loop towards the opposite saturation point. Since thisreversal is Iautomatic and no curs each time the core saturates, thesystem operates as a very low frequency oscillator with traverse of thecomplete hysteresis loop for each half cycle.

In summary, the low frequency magnetic oscillator of this invention usesthe principle of applying a very slightly unbalanced alternating currentto a saturable magnetic core in order to produce an exceptionally longsaturation time. This magnetic core together with the associatedcircuitry described, permits long oscillations on the order of fiveminutes per cycle to be obtained.

Many changes and modifications of this invention will undoubtedly occurto those who are skilled in the art, and I therefore wish it to beunderstood that I intend to be limited by the scope of the appendedclaims and not by the specific embodiment of my invention which isdisclosed herein for the purpose of illustration only.

I claim:

1. Low frequency oscillator apparatus comprising: saturable magneticcore means; a source of alternating current potential; a source ofdirect current potential;

first asymmetric current fiow circuit means conductive in one directionand having a first control member; second asymmetric current flowcircuit means conductive in a direction opposite to said first circuitmeans and having a second control member; control means interconnectingsaid first and second circuit means effective upon sensing an increasein current in one of said circuit means to render the othernonconductive; connective means comprising said first and secondasymmetric circuit means connecting said alternating current potentialin energizing relation to said saturable core means; polarity reversingswitching means having control and switching electrodes, said switchingelectrodes interconnecting said direct current potential to saidsaturable magnetic core means to reverse the polarity of said directcurrent po tential upon a signal being applied to said controlelectrodes; and means connecting said control electrodes to saidconnective means for causing the reversal of the polarity of said directcurrent source upon each occurrence of said control means rendering oneof said circuit means nonc-onductive.

2. Low frequency oscillator apparatus comprising: saturable magneticcore means; a source of alternating current potential; a source ofdirect current potential; first asymmetric current flow circuit meansconductive in one direction and having a first control member; secondasymmetric current fiow circuit means conductive in a direction oppositeto said first circuit means and having a second control member; controlmeans interconnecting said first and second circuit means and effectiveupon sensing an increase in current in either one of said circuit meansto render the other nonconductive; connective means comprising saidfirst and second asymmetric circuit means connecting said alternatingcurrent potential in energizing relation to said saturable core meanswhereby positive half cycles of said alternating current flow throughsaid first circuit means and the negative half cycles iiow through saidsecond circuit means; polarity reversing switching means having controland switching electrodes; said switching electrodes interconnecting saiddirect current potential to said saturable magnetic core means inenergizing relation thereto, said switching means being operative toreverse the polarity of said direct current potential upon a signalbeing applied to said control electrodes; and means connecting saidcontrol electrodes to said connective means to sense the elfect of saidincrease in current and provide a signal in response thereto to operatesaid switching means causing the reversal of the polarity of said directcurrent source.

3. Low frequency oscillator apparatus comprising: saturable magneticcore means; a source of alternating current potential; a source ofdirect current potential; first normally conductive asymmetric currentflow circuit means conductive in one direction and having a firstcontrol member; second normally conductive asymmetric current fiowcircuit means conductive in a direction opposite to said first circuitmeans and having a second control member; connective means comprisingsaid first and second asymmetric circuit means connecting saidalternating current potential in energizing relation to said saturablecore means; polarity reversing switching means having control andswitching electrodes, said switching electrodes interconnecting saiddirect current potential to said saturable magnetic core means, saiddirect current in effect unbalancing said alternating current to causethe core flux to move slowly to saturation in a series of minorhysteresis loops; control means interconnecting said first and secondcircuit means and efiective upon the current exceeding a predeterminedmagnitude in one of said circuit means as a result of reachingsaturation to render the other asymmetric circuit means nonconductive;and means connecting said control electrodes to said connective meansfor causing the reversal of the polarity of said direct current sourceupon occurrence of said control means rendering one of said circuitmeans nonconductive.

4. Low frequency oscillator apparatus comprising: saturable magneticcore means; a source of alternating current potential; a source ofdirect current potential; first and second normally conductiveunidirectional current paths, said second current path being conductivein the opposite direction than said first current path; first circuitmeans comprising said first and second current paths connecting saidalternating current source in energizing relation to said saturable coremeans; second circuit means connecting said direct current potential inenergizing relationship to said saturable magnetic core means; polarityreversing switching means in said second circuit means having controland switching electrodes, said switching electrodes being connected toreverse the polarity of said source of direct current potential to saidsaturable magnetic core rneans upon a signal being applied =to saidcontrol electrodes; control means interconnecting said first and secondcurrent paths and effective upon an increase in current in one of saidpaths to render the other of said paths nonconductive; and meansconnecting said control electrodes to said first circuit means to sensesaid increase in current and operate the switching means to cause thereversal of the polarity of said direct current source in responsethereto.

5. Low frequency oscillator apparatus comprisin saturabie magnetic coremeans; a source of alternating current potential; a source of directcurrent potential; first and second normally conductive unidirectionalcurrent paths, said second current path being connected to conduct inthe opposite direction than said first current path;

first circuit means comprising said first and second ourrent pathsconnecting said alternating current source in energizing relation tosaid 'saturable core means; second circuit means connecting said directcurrent potential in energizing relation to said saturable magnetic coremeans; polarity reversing switching means in said second circuit meanshaving control and switching electrodes, said switching electrodes beingoperable to reverse the polarity of said source of direct currentpotential to said saturable magnetic core means; control meansinterconnecting said first and second current paths and effective uponan increase in current in one of said paths which signifies sat uration.of said core means to render the other of said paths conductive; meansconnecting said control electrodes to said first circuit means to sensesaid increase in current and operate the switching means to cause there- 7 versal of the polarity of said' direct current source in responsethereto; and current control means responsive current path.

6. Low frequency oscillator apparatus comprising: saturable magneticcore means; a source of alternating current potential of suflicientamplitude to accomplish a change in the flux of said magnetic core meansbut of insufficient magnitude to saturate said core means; a source ofdirect current potential of small magnitude compared to said alternatingcurrent potential; first and second normally conductive unidirectionalcurrent paths, said second current path being connected to conduct inthe opposite direction than said first current path; first circuit meanscomprising said first and second current paths connecting saidalternating current source in en ergizing relation to said saturablecore means; second circuit means connecting said direct currentpotential in ener izing relation to said saturable magnetic core meansthereby causing a slight unbalance in the alternating current such thatthe core flux moves slowly towards saturation in a series of minor.hysteresis loops; polarity reversing switching means in said secondcircuit means having control and switching electrodes, said switchingelectrodes being connected to reverse the polarity of said source ofdirect current potential to said saturable magnetic core means upon asignal being applied to said control electrodes; control meansinterconnecting said first and'second current paths and efi'ective uponsaturation of said core means signified by an increase in current in oneof said paths to render andinaintain the other of said pathsnonconductive; and means connecting saidcontrol electrodes to said firstcircuit means to sense said increase in current and operate theswitching means to cause the reversal of the polarity of said directcurrent source in response thereto. i

No references cited;

1. LOW FREQUENCY OSCILLATOR APPARATUS COMPRISING: SATURABLE MAGNETICCORE MEANS; A SOURCE OF ALTERNATING CURRENT POTENTIAL; A SOURCE OFDIRECT CURRENT POTENTIAL; FIRST ASYMMETRIC CURRENT FLOW CIRCUIT MEANSCONDUCTIVE IN ONE DIRECTION AND HAVING A FIRST CONTROL MEMBER; SECONDASYMMETRIC CURRENT FLOW CIRCUIT MEANS CONDUCTIVE IN A DIRECTION OPPOSITETO SAID FIRST CIRCUIT MEANS AND HAVING A SECOND CONTROL MEMBER; CONTROLMEANS INTERCONNECTING SAID FIRST AND SECOND CIRCUIT MEANS EFFECTIVE UPONSENSING AN INCREASE IN CURRENT IN ONE OF SAID CIRCUIT MEANS TO RENDERTHE OTHER NONCONDUCTIVE; CONNECTIVE MEANS COMPRISING SAID FIRST ANDSECOND ASYMMETRIC CIRCUIT MEANS CONNECTING SAID ALTERNATING CURRENTPOTENTIAL IN ENERGIZING RELATION TO SAID SATURABLE CORE MEANS; POLARITYREVERSING SWITCHING MEANS HAVING CONTROL AND SWITCHING ELECTRODES, SAIDSWITCHING ELECTRODES INTERCONNECTING SAID DIRECT CURRENT POTENTIAL TOSAID SATURABLE MAGNETIC CORE MEANS TO REVERSE THE POLARITY OF SAIDDIRECT CURRENT POTENTIAL UPON A SIGNAL BEING APPLIED TO SAID CONTROLELECTRODES; AND MEANS CONNECTING SAID CONTROL ELECTRODES TO SAIDCONNECTIVE MEANS FOR CAUSING THE REVERSAL OF THE POLARITY OF SAID DIRECTCURRENT SOURCE UPON EACH OCCURRENCE OF SAID CONTROL MEANS RENDERING ONEOF SAID CIRCUIT MEANS NONCONDUCTIVE.